Proton conductor and method for manufacturing the same, and electrochemical device

ABSTRACT

A proton conductor, a method for manufacturing the same, and an electrochemical device using the proton conductor are provided. The proton conductor includes a carbon derivative which has a carbon material selected from the group consisting of a fullerene molecule, a cluster consisting essentially of carbon, a fiber-shaped carbon and a tube-shaped carbon, and mixtures thereof; and at least a proton dissociative group, the proton dissociative group being bonded to the carbon material via a cyclic structure of tricyclic or more. The method includes the steps of obtaining the carbon derivative, hydrolyzing the derivative with alkali hydroxide, subjecting the hydrolyzed product to ion exchange, and forming a group with proton-dissociating properties.

RELATED APPLICATION DATA

The present application claims priority to Japanese Patent ApplicationNo. P2001-313995 filed on Oct. 11, 2001 and Japanese Patent ApplicationNo. P2002-138210 filed on May 14, 2002. The above-referenced Japanesepatent applications are incorporated herein by reference to the extentpermitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to a proton conductor and a method formanufacturing the proton conductor, and also relates to anelectrochemical device.

On-going efforts continue in an attempt to develop the fuel cell becauseattention is focused on the fuel cell as an environment-orientedelectric energy generating system for the next generation from thereasons such as its high efficiency and cleanliness with respect topower generation.

Fuel cell can be roughly divided according to the types of protonconductor used in it because the operating temperature and the conditionin use exert strong influence on the property of the proton conductor.Because the property of the proton conductor in use gives stronginfluence on performance characteristics of the fuel cell, it isessential to improve performance of the proton conductor in order tohave the fuel cell with better performance characteristics.

In general, in the temperature range from normal temperature to lowerthan 100° C., proton-conductive macromolecular film is used, which hassolid macromolecular film. Typical examples include NAFION (trade name;DU PONT De NEMOURS & CO.) or GORE FILM (GORE & ASSOCIATES). These areperfluorosulfonic acid resins, and efforts continue in an attempt tomake modifications and improvements of these types of products. Inaddition to these perfluoro type resins, hydrocarbon type macromolecularfilm have been known in recent years.

Also, as relatively new types of inorganic metal oxide type protonconductor, polymolybdic acids or oxides having a large amount ofconductor, polymolybdic acids or oxides having a large amount of waterof hydration such as H₃M₁₂PO₄₀.29H₂O (M=Mo,W) or Sb₂O₅.nH₂O are known.

When these macromolecular materials or hydrated compounds are placedunder humid conditions, they exhibit high proton conductive propertynear normal temperature. Specifically, if an example is taken onperfluoro-sulfonic acid resin, protons electrolytically dissociated fromsulfonic group are bonded with moisture which is extensively containedin macromolecular matrix (hydrogen bonding), and protonized water, i.e.oxonium ions (H₃O⁺) are generated. Because protons in form of oxoniumions can smoothly migrate in macromolecular matrix, matrix material ofthis type can provide considerably high proton conductive effect even atnormal temperature.

On the other hand, a proton conductor with conductive mechanism entirelydifferent from these has been recently developed. Specifically, it hasbeen found that complex metal oxides with perovskite structure such asSrCeO₃ doped with Yb have proton conductivity even when moisture is notused as migration medium. It appears that, in the complex metal oxides,protons are conducted through channel between oxygen ions, which formskeletons of the perovskite structure.

In this case, it is not that conductive protons are present in thecomplex metal oxides from the beginning. It is believed that, when theperovskite structure is brought into contact with vapor contained inatmospheric gas in the surroundings, water molecules at high temperaturereact with oxygen-lacking portion in the perovskite structure by doping,and protons are generated only when this reaction takes place.

However, in the proton conductor as described above, there are a numberof problems.

For example, the matrix material such as perfluorosulfonic acid resinmust be continuously maintained under sufficiently humid conditionduring use in order to keep proton conductive property at high level.Also, for the purpose of preventing freezing or boiling of watercontained in the matrix, the range of the operating temperature shouldnot be wide.

In case of inorganic metal oxide proton conductor such asH₃M₁₂PO₄₀.29H₂O (M=Mo,W) or Sb₂O₅.nH₂O, temperature must be maintainedhigh in order to keep structural water contained therein so thatsignificant proton conduction is carried out. Also, in a certain type ofperovskite oxide such as SrCeO₃, operating temperature must be kept athigh level, i.e. 500° C. or higher. When humidity is low, protonconductivity rapidly decreases.

As described above, the conventional type proton conductor depends muchon the atmospheric conditions, e.g. moisture must be supplied or vaporis needed. Moreover, there are problems that operating temperature istoo high or temperature range is too narrow.

Therefore, humidifier or other types of accessory equipment or deviceare needed for a system such as fuel cell. This unavoidably requires thedesigning of the system in larger size or higher cost for systemconstruction. A need, therefore, exists to provide an improved protonconductor and methods of making and using same.

SUMMARY OF THE INVENTION

The present invention provides an improved proton conductor, a methodfor manufacturing the same, and an electrochemical device, which can beused even under dry atmosphere or in relatively wide temperature rangeincluding room temperature, and by which it is possible to extensivelyimprove proton conductivity.

In an embodiment, a proton conductor includes a carbon derivative whichhas a carbon material that includes, for example, a fullerene molecule,a cluster consisting essentially of carbon, a fiber-shaped carbon, atube-shaped carbon, the like and mixtures thereof, and at least a protondissociative group, the proton dissociative group being bonded to thecarbon material via a cyclic structure, such as tricyclic or more.

As used herein, the term, “a group with proton (H⁺)-dissociatingproperty” or other like term means a group, from which protons can beionized or electrolytically dissociated. Also, the term“proton-dissociating” or the like means that protons are separated byionizing or electrolytic dissociation.

In another embodiment, the present invention provides a proton conductorincluding a carbon derivative which has a carbon material that includes,for example, a fullerene molecule, a cluster consisting essentially ofcarbon, a fiber-shaped carbon, a tube-shaped carbon, the like andmixtures thereof; and a functional group, having proton-dissociatingproperty. In this regard, the proton conductor of the present inventionis less dependent on atmosphere and exhibits high proton conductiveproperty even in dry air or in wide temperature range including hightemperature, and it can be continuously used. Even when moisture ispresent, this is not problematic to the performance of the protonconductor according to an embodiment of the present invention.

The functional group as described above is bonded to the carbon materialvia a cyclic structure such as tricyclic or more. In this regard, it ispossible to attain high heat-resistant property and high chemicalstability.

In still another embodiment, the present invention provides a method formanufacturing a proton conductor, the method including the steps ofobtaining a carbon derivative which has a carbon material selected fromthe group consisting of a fullerene molecule, a cluster consistingessentially of carbon, a fiber-shaped carbon and a tube-shaped carbon,and mixtures thereof, and a functional group, having an ester group as aprecursor of a group with proton-dissociating property, the functionalgroup being bonded to the carbon material via a cyclic structure oftricyclic or more; hydrolyzing the derivative with alkali hydroxide; andforming a group with proton-dissociating property through ion exchangeof the hydrolyzed product.

According to the method for manufacturing the proton conductor, it ispossible to manufacture the proton conductor of the present inventionhaving excellent properties as described above in easy and efficientmanner and to reduce the cost for the manufacture. Also, it is possibleto manufacture the product on mass-production basis.

In yet another embodiment, the present invention provides anelectrochemical device, having a first electrode, a second electrode,and a proton conductor sandwiched or disposed between these twoelectrodes, wherein the proton conductor includes a carbon derivativewhich has a carbon material that includes, for example, a fullerenemolecule, a cluster consisting essentially of carbon, a fiber-shapedcarbon, a tube-shaped carbon, the like and mixtures thereof; and atleast a proton dissociative group, the proton dissociative group beingbonded to the carbon material via a cyclic structure, such as tricyclicor more.

According to the electrochemical device of the present invention, theproton conductor sandwiched between the first electrode and the secondelectrode includes the derivative serving as the proton conductor of thepresent invention with excellent properties as described above. As aresult, it can provide the same effects as those of the proton conductorof the present invention. No humidifier is required, and it is possibleto design the system in small size and in simple structure.

In a further embodiment, the present invention provides a protonconductor including a carbon derivative which has a carbon material thatincludes, for example, a fullerene molecule, a cluster consistingessentially of carbon, a fiber-shaped carbon, a tube-shaped carbon, thelike and mixtures thereof, and at least one group of formula (1) or (2),the group being bonded to the carbon material,

wherein X¹, X², X³ and X⁴ independently represent of each other a protondissociative group, and A¹ and A² independently represent of each other—O—, —R—, —O—R—, —R—O—, —O—R—O—, or —R—O—R— where R is an alkyl grouprepresented by C_(x)H_(y), wherein x represents an integer of 1 to 20,and y represents an integer of 0 to 40.

In an embodiment, the present invention provides a proton conductorincluding a carbon derivative which has a carbon material that includesa fullerene molecule, a cluster consisting essentially of carbon, afiber-shaped carbon, a tube-shaped carbon, the like and mixturesthereof, and at least a group of formula (3), the group being bonded tothe carbon material,

wherein X⁵ and X⁶ independently represent of each other a protondissociative group, and A³ and A⁴ independently represent of each other—O—, —R′—, —O—R′—, —R′—O—, —O—R′—O—, —R′—O—R″— (R′ and R″ are alkylgroups represented by C_(x′)C_(y′)H_(z′), wherein x′ represents aninteger of 1 to 20, y′ represents an integer of 1 to 40, and z′represents an integer of 0 to 39.

In this case also, from the reasons as described above, chemicalstability of the material is extensively improved and the material hashigh heat-resistant property.

In another embodiment, the present invention provides a proton conductorcontaining a carbon material expressed by the following molecularformula (1) or (2):C₆₀═(C(PO(OH)₂)₂)_(n)  Molecular formula (1)C₆₀═(C(SO₃H)₂)_(n)  Molecular formula (2)

(where n in the molecular formula (1) and (2) represents a number of 1to 30).

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A represents a general scheme of a proton conductor according toan embodiment of the present invention.

FIG. 1B represents a general scheme of a proton conductor according toan embodiment of the present invention.

FIGS. 2A and 2B show a general scheme of the proton conductor (FIG. 2A)and a reaction scheme (FIG. 2B) of an example of a method formanufacturing the proton conductor according to an embodiment of thepresent invention.

FIG. 3 is a schematic drawing showing a mechanism of proton conductionin a fuel cell according to an embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of an example of a fuel cellaccording to an embodiment of the present invention.

FIGS. 5A and 5B represent schematic drawings showing fullerenemolecules, which serve as base materials in a proton conductor accordingto an embodiment of the present invention.

FIG. 6 shows various examples of carbon clusters, which serve as basematerials in the proton conductor according to an embodiment of thepresent invention.

FIG. 7 shows schematic drawings of examples of carbon clusters includingpartial fullerene structures according to an embodiment of the presentinvention.

FIG. 8 represents schematic drawings showing examples of carbon clustersincluding diamond structures according to an embodiment of the presentinvention.

FIG. 9 represents schematic drawings of carbon clusters includingclusters bonded to each other according to an embodiment of the presentinvention.

FIGS. 10A–10C represent drawings of carbon nanotube and carbon fibers,which serve as base materials for the proton conductor according to anembodiment of the present invention.

FIG. 11 is a graph showing the results of measurement of FT-IR accordingto an embodiment of the present invention.

FIG. 12 is a graph showing measurement results of TG-DTA according to anembodiment of the present invention.

FIG. 13 is a graph showing measurement results of RGA according to anembodiment of the present invention.

FIG. 14 is a diagram of an equivalent circuit according to an embodimentof the present invention.

FIG. 15 is a graph showing measurement results of complex impedance ofphosphoric acid type fullerene derivative aggregate pellets according toan embodiment of the present invention.

FIG. 16 is a graph showing measurement results of FT-IR according to anembodiment of the present invention.

FIG. 17 is a graph showing measurement results of complex impedance ofsulfonic acid type fullerene derivative aggregate pellets according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a proton conductor, an electrochemicaldevice employing same, and methods of manufacturing and using same.

As shown in the general schemes of the proton conductor of the presentinvention in FIG. 1A and FIG. 1B, the functional group having a groupwith proton-dissociating property expressed by the general formula (1)or (2) is bonded via the tricyclic structure to the base material, intowhich the functional group is to be introduced. As a result, the cyclicstructure is stable, and there are two or more bonding sites. Even whenthe bonding may be broken up, radicals can be bonded again. Chemicalstability of the material is extensively improved and the material hashigh heat-resistant property. The functional group may be bonded via thetricyclic structure or via a cyclic structure of tricyclic or more. Insuch case, it is possible to further improve chemical stability andheat-resistant property.

In the general formula (1) and (2), it is preferable that at least oneof the groups with proton-dissociating property is, for example,—PO(OH)₂, —SO₃H, —COOH or the like. In the general formula (2), at leastone of the groups with proton-dissociating property includes —OSO₃H orthe like.

The number of the functional groups to be bonded to one base materialcan be controlled in the range from 1 to 30 by adjusting molar ratio ofthe raw material serving as the base material during synthesis and theother raw materials added to it. For instance, it is possible to add thefunctional groups to all of the double bonds on the base material. Themore the number of the functional groups on the base material is, themore the number of protons is increased, and the more the conductivityis increased.

In an embodiment, the present invention provides a proton conductorincluding a carbon derivative which has a carbon material that includesa fullerene molecule, a cluster consisting essentially of carbon, afiber-shaped carbon, a tube-shaped carbon, the like and mixturesthereof; and

-   -   at least a group of formula (3), the group being bonded to the        carbon material,

wherein X⁵ and X⁶ independently represent of each other a protondissociative group, and A³ and A⁴ independently represent of each other—O—, —R′—, —O—R′—, —R′—O—, —O—R′—O—, —R′—O—R″—R′ and R″ are alkyl groupsrepresented by C_(x′)F_(y′)H_(z′), wherein x′ represents an integer of 1to 20, y′ represents an integer of 1 to 40, and z′ represents an integerof 0 to 39.

In this case also, from the reasons as described above, chemicalstability of the material is extensively improved and the material hashigh heat-resistant property.

In the general formula (3) as described above, it is preferable that atleast one of the groups with proton-dissociating property is —PO(OH)₂,—SO₃H, —COOH or the like.

When the radical —PO(OH)₂ is used as the group with proton-dissociatingproperty as described above, the number of protons to be dissociated foreach functional group bonded to the base material is four. Therefore, itis possible to attain high proton conductivity and also to extensivelyimprove chemical stability. When the radical —SO₃H is used,proton-dissociating property is higher, and it is possible to attainhigher proton conductivity.

In another embodiment, the present invention provides a proton conductorcontaining a carbon material expressed by the following molecularformula (1) or (2):C₆₀═(C(PO(OH)₂)₂)_(n)  Molecular formula (1)C₆₀═(C(SO₃H)₂)_(n)  Molecular formula (2)

(where n in the molecular formula (1) and (2) represents a number of 1to 30).

FIG. 2A represents a general scheme of the derivative serving as theproton conductor according to an embodiment of the present invention,which is expressed by the molecular formula (1), i.e.C₆₀═(C(PO(OH)₂)₂)_(n) (where n=2).

As shown in FIG. 2A, to the carbon atoms to constitute the fullerenemolecule (C₆₀), serving as the base material where the functional groupsare to be introduced, the functional groups are bonded via a tricyclicstructure. As a result, chemical stability of the material isextensively improved and the material has high heat-resistant property.Also, the radical —PO(OH)₂ is used as the group with proton-dissociatingproperty. Because the number of the protons to be dissociated per eachfunctional group bonded to the fullerene molecule is four, it ispossible to attain high proton conductivity.

The method for manufacturing the proton conductor of the presentinvention as shown in FIG. 2A can be expressed, for instance, by thereaction scheme shown in FIG. 2B.

First, the fullerene molecule (C₆₀) and tetraethyl methylenediphosphonate are allowed to react under the presence of iodine and NaI.Then, it is possible to obtain a derivative where the functional groupwith ester group serving as a precursor of the group withproton-dissociating property is bonded to the fullerene molecule via thetricyclic structure.

Next, the derivative thus obtained is hydrolyzed using alkali hydroxide,e.g. sodium hydroxide. Then, the hydrolyzed product is subjected to ionexchange, and the proton conductor of the present invention can beobtained, in which the functional groups having the radial —PO(OH)₂ asthe group with proton-dissociating property are bonded to the fullerenemolecule (C₆₀) via tricyclic structure.

According to the manufacturing method in an embodiment of the presentinvention, it is possible to manufacture the proton conductor of thepresent invention having excellent properties in easy and efficientmanner and to reduce the manufacturing cost. Also, it is possible tosynthesize the product on mass-production basis.

The proton conductor of the present invention can be used in varioustypes of electrochemical devices. Specifically, in a basic structurehaving a first electrode, a second electrode, and a proton conductorsandwiched between these two electrodes, the proton conductor of thepresent invention can be preferably applied to the proton conductor.

In an embodiment, the proton conductor of the present invention can beapplied to an electrochemical device where the first electrode and/orthe second electrode is a gas electrode, or to an electrochemical devicewhere an active material electrode is used as the first electrode and/orthe second electrode.

Description will be given below on examples where the proton conductorof the present invention is applied to a fuel cell where fuel issupplied to the first electrode and oxygen is supplied to the secondelectrode.

The mechanism of the proton conduction in the fuel cell is asschematically shown in FIG. 3. A proton conductive portion 1 issandwiched between the first electrode (e.g. hydrogen electrode) 2 andthe second electrode (e.g. oxygen electrode) 3. The dissociated protons(H⁺) are moved from the first electrode 2 toward the second electrode 3in arrow direction.

FIG. 4 shows a concrete example of a fuel cell using the protonconductor of the present invention. The fuel cell has a negativeelectrode (fuel electrode or hydrogen electrode) 2 and a positiveelectrode (oxygen electrode) 3 with terminals 8 and 9 respectively andopposing to each other and having a catalyst 2 a and a catalyst 3 aclosely fitted or dispersed, and a proton conductive portion 1 issandwiched between the two electrodes. When in use, hydrogen is suppliedthrough an inlet 12 on the negative electrode 2 side, and it isdischarged through an outlet 13 (which may not be provided). While thefuel (H₂) 14 is passed through a passage 15, protons are generated.These protons are moved toward the positive electrode 3 together withthe protons generated at the proton conductive portion 1. Then, theprotons react with oxygen (air) 19, which is supplied through an inlet16 and is directed toward an outlet 18 though a passage 17. As a result,electromotive force as desired is obtained.

In the fuel cell with the arrangement as described above, protons aredissociated at the proton conductive portion 1, and the protons suppliedfrom the negative electrode 2 are moved toward the positive electrode 3,and this makes it possible to provide higher proton conductivity.Therefore, no additional apparatus such as humidifier is required, andthis makes it possible to design the system in simplified andlightweight construction.

There is no special restriction on the fullerene molecule, serving asthe base material where the functional groups are to be introduced sofar as it is a spherical cluster molecule. In general, a fullerenemolecule selected from C₃₆, C₆₀, (FIG. 5A), C₇₀ (FIG. 5B) C₇₆, C₇₈, C₈₀,C₈₂, C₈₄, C₈₆, C₈₈, C₉₀, C₉₂, C₉₄, C₉₆, the like or a mixture of twotypes or more of these molecules is preferably used.

These fullerene molecules were discovered in mass analysis spectrum ofcluster beam by laser ablation of carbon. (Kroto, H. W; Heath, J. R.;O'Brien, S. C.; Curl, R. F; Smalley, R. E.: Nature, 1985; 318, 162.).The manufacturing method of same has been established. For example, themanufacturing method based on arc discharge of carbon electrode has beenestablished to date. Attention also has been focused on the fullerene asthe material of carbon semiconductor.

For instance, when a large quantity of the derivatives are aggregated,which are obtained by bonding the functional group to the fullerenemolecule via a cyclic structure of tricyclic or more, the protonconductive property provided with the derivatives as bulk can becontinuously used even at low humidity atmosphere because protonsderived from the group with proton-dissociating property originallycontained in the molecule are directly involved in the migration.

The fullerene molecule as described above particularly has electrophilicproperty, and this seems to extensively contribute to the promotion ofionizing or electrolytic dissociation of hydrogen ions in the group withproton-dissociating property with high acidity, and it exhibits highproton conductive property. Also, a considerable number of functionalgroups can be bonded to one fullerene molecule via cyclic structure oftricyclic or more. As a result, the number of protons related to theconduction per unit volume of the conductor is extremely increased, andthis contributes to the attainment of higher conductivity.

The derivative serving as the proton conductor according to the presentinvention has carbon atoms of the fullerene molecules in almost allcases. It is lightweight, resistant to deterioration and contains nocontaminated substance. The manufacturing cost of the fullerene moleculeis now being rapidly decreased. From the viewpoints of resource,environment and economy, the fullerene molecule is regarded as avirtually ideal carbon material, being better than any other types ofmaterial.

The fullerene derivative thus obtained can be produced in form of filmby coating, rolling or other film-forming method, and this can beapplied to the proton conductor to be used in the electrochemical deviceof the present invention.

The proton conductor may substantially have the fullerene derivativeonly or it may be bonded using a binder. Further, two or more fullerenederivatives may be bonded together directly or indirectly, and a polymermay be formed.

In case the proton derivative substantially has the fullerene derivativeonly, the fullerene derivative may be press-molded to a film-like protonconductor, and this can be used. When the fullerene derivative bondedtogether using the binder is used as the proton conductor, it ispossible to form the proton conductor with high strength by using thebinder.

As the macromolecular material to be used as the binder, one type or twotypes or more of the polymers having the film-forming property publiclyknown may be used. The proton conductor of this type can also providethe same proton conductive property as that of the proton conductor,which has only the fullerene derivative.

Moreover, unlike the case where the fullerene derivative is used alone,the film-forming property derived from the macromolecular material isprovided. Compared with the powder compressed molded product of thefullerene derivative, it has higher strength and high gas-permeationpreventing ability, and it can be used as a flexible proton conductivethin-film (normally, with thickness of not more than 300 micrometers).

There is no special restriction on the macromolecular material so far asit does not inhibit proton conductive property (by reaction with thefullerene derivative) and has good film-forming property. Normally, thematerial having no electronic conduction property and having goodstability is used. For example, polyfluoroethylene, polyvinylidenefluoride, polyvinyl alcohol, the like or combinations thereof may bepreferably used. These are preferable to use as the macromolecularmaterials also from the reasons given below.

First, polytetrafluoroethylene is preferably used because, only using asmall quantity, it can easily form thin film with higher strengthcompared with other types of macromolecular materials. In this case, themixing quantity is not more than about 3 weight %, or more preferablyabout 0.5 to about 1.5 weight %. The thickness of the thin film can benormally as thin as about 100 micrometers to about 1 micrometer

Further, polyvinylidene fluoride or polyvinyl alcohol is preferably usedbecause it is possible to obtain proton conductive thin film havingexcellent gas-permeation preventing ability. The mixing quantity in thiscase is preferably in the range of about 5 to about 15 weight %.

Whether it is polyfluoroethylene or polyvinylidene fluoride or polyvinylalcohol, if the mixing quantity is lower than the lower limit of therange as given above, sufficient film-forming strength may not beprovided.

To obtain the thin film of the proton conductor of the presentinvention, produced by bonding the fullerene derivative using binder,press molding, extrusion molding, or other film-forming method alreadyknown may be used.

The electrochemical device according to the present invention canprovide full functions in atmospheric air. Thus, electrochemical energycan be efficiently obtained without adjusting pressure, temperature,humidity, or the like when it serves as the fuel cell.

Also, the derivative is obtained by bonding the functional groups to thecarbon atoms (which constitute the fullerene molecule) via the cyclicstructure of tricyclic or more, and this is used as the compositematerial of the proton conductor. Accordingly, unlike the case whereH₃O⁺ ion conductor NAFION is used, it can fulfill the function withoutrequiring humidifier or in atmospheric air and under low humiditycondition.

Specifically, electrochemical energy can be obtained in the atmosphericair under low humidity condition, and not much time is required untilsteady operation is reached. This can make the starting operation fasterwhen it is used as the fuel cell. The humidifier may be provided and theoperation may be performed under the presence of moisture, but no suchcondition is required in the present invention.

When H₃O⁺ ion conductor NAFION is used, in addition to the watergenerated at the generation of electrochemical energy, water generatedby migration is present at the positive electrode, and dehumidifier isrequired. In the embodiment of the present invention, hydrogen gas issupplied to the negative electrode side and electrolysis is performed.The protons generated by electrolysis are moved toward the positiveelectrode via the proton conductor of the present invention and areallowed to react with oxygen, and electrochemical energy can beobtained. Accordingly, electrochemical energy can be generated withoutrequiring dehumidifier.

Therefore, the electrochemical device of the present invention is adevice in compact size and suitable for general-purpose application.

In the present invention, instead of the derivative using the fullerenemolecule as the base material, cluster derivative may be used. Forinstance, a cluster having carbon powder is obtained by arc dischargemethod of carbon electrode, and the functional groups are bonded to thecluster via cyclic structure of tricyclic or more.

Here, the cluster normally means an aggregate, which has several toseveral hundreds of atoms bonded or aggregated together. Protonconductive performance is improved by this aggregate, and high filmstrength can be provided while maintaining good chemical property, andlayers can be easily formed. Also, the cluster has carbon atoms as maincomponents. It is an aggregate where several to several hundreds ofcarbon atoms are bonded together regardless of the type of carbon-carbonbonding. However, it does not necessarily have carbon cluster by 100%,and other types of atoms may be mixed. Including such case, an aggregatewhere carbon atoms are present as majority is called as a carboncluster.

The main component of the proton conductor according to the presentinvention is a substance, which is obtained by bonding the functionalgroup to the carbon cluster serving as the base material via a cyclicstructure of tricyclic or more. In this respect, protons can be easilydissociated under dry condition, and the effects similar to the protonconductor having fullerene derivative as described above can be providedincluding the proton conductive property. Moreover, many types ofcarbonaceous materials are included in the category of the carboncluster, and carbonaceous materials can be selected from the materialsin much wider range.

In this case, the carbon cluster is used as the base material. A largequantity of the functional group having a group of proton-dissociatingproperty must be bonded in order to provide better proton conductiveproperty, and this can be accomplished by the carbon cluster. However,this makes the acidity of solid proton conductor extremely higher.Unlike normal carbonaceous material, carbon cluster is resistant tooxidizing, deterioration and has high durability. The atoms are closelybonded together. Thus, even when the acidity is high, the bondingbetween the atoms is not broken up (i.e. highly resistant to chemicalchange), and film structure can be maintained well.

The proton conductor with the above arrangement can provide high protonconductive property even under dry condition. As shown in FIG. 6 to FIG.9, there are various types, and it can be selected from wide range ofmaterials as the raw material of the proton conductor.

FIG. 6 shows various types of carbon clusters where a large number ofcarbon atoms are bonded together, showing spherical or elongatedspherical shape or closed surface structure similar to these. (In thefigure, molecular type fullerene is also shown.) In contrast, FIG. 7shows various types of carbon clusters, in each of which a part of thespherical structure is missing. In this case, the cluster ischaracterized in that there is an open end in the structure. Suchstructures are often seen as side products in the process to manufacturethe fullerene by arc discharge. When carbon atoms in most of the carbonclusters have SP3-bonding, this leads to various types of clustershaving diamond structure as shown in FIG. 8.

The cluster where most of the carbon atoms are bonded by SP2-bonding hasplane structure of graphite, or it has the whole or a part of thestructure of fullerene or nanotube. The cluster having the structure ofgraphite has electronic conductive property in the cluster, and this isnot preferable to use as the base material of the proton conductor.

In contrast, SP2-bonding of fullerene or nanotube partially contains thefeatures of SP3-bonding and often has no electronic conductive property.Thus, it is preferable to use as the base material of the protonconductor.

FIG. 9 shows various cases where the clusters are bonded with eachother, and these types of structures can also be applied in the presentinvention.

The carbon cluster derivative can be directly press-molded in form offilm or pellet without binder. In the present invention, the carboncluster serving as the base material has preferably a length of not morethan 100 nm, or more preferably not more than about 100 angstroms. Thenumber of the groups to be introduced is preferably 2 or more.

Further, as the carbon cluster, it is preferable to use a cage-likestructure (such as the fullerene molecule as described above) or astructure having an open end at least on a part of it. Such fullerene ofdefective structure has reactivity of the fullerene molecule, and themissing portion, i.e. open portion, has higher reactivity. Therefore,the introduction of the functional groups with the group withproton-dissociating property can be promoted, and high functional groupintroducing ratio and higher proton conductive property can be obtained.Compared with the fullerene molecule, this can be synthesized in largerquantity, and this results in the production at very low cost.

On the other hand, it is preferable to use a structure of tubular orlinear carbon structure as the base material of the proton conductor ofthe present invention. As the tubular carbon structure, tube-likestructure, e.g. carbon nanotube, may be preferably used. Also, as thelinear carbon structure, fiber-like structure, e.g. carbon fiber, may bepreferably used.

In the carbon nanotube or the carbon fiber, electrons can be easilydischarged because of the structure, and surface area can be extremelyincreased. This contributes to the improvement of proton propagationefficiency.

The carbon nanotube or the carbon fiber preferably used in this case canbe manufactured by arc discharge method, chemical vapor phase growingmethod (thermal CVD method) or other suitable processes.

In the arc discharge method, for instance, a metal catalyst, such asFeS, Ni, Co, or the like is used, and synthesis is performed underhelium atmosphere (e.g. 150 Torr) using an arc discharge chamber. Thematerial is attached on inner wall of the chamber in cloth-like form byarc discharge, and the carbon nanotube can be obtained. When the abovecatalysts are used together, the carbon nanotube with smaller diametercan be obtained. When arc discharge is performed without catalysts, acarbon nanotube of multi-layer type with larger diameter can beprepared.

As described above, the material can be formed by arc discharge withouta catalysts. The graphene structure (cylindrical structure) ofmulti-layer nanotube as shown in the perspective view of FIG. 10A andthe partial cross-sectional view of FIG. 10B represents a carbonnanotube with high quality and without defect. It is known that this isa material with very high performance characteristics as electronreleasing material.

As described above, the derivative is obtained by bonding the functionalgroup with a group with proton-dissociating property to the carbonnanotube obtained by arc discharge method via a cyclic structure oftricyclic or more, and this derivative also has high proton conductiveproperty even under dry condition.

The chemical vapor phase growing method is a method to synthesize thecarbon nanotube or the carbon fiber by the reaction of transition metalparticles with hydrocarbon such as acetylene, benzene, ethylene, CO orthe like. A transition metal substrate or a coated substrate is allowedto react with hydrocarbon or CO gas, and the carbon nanotube or thecarbon fiber are stacked on the substrate.

For instance, a Ni substrate is placed in an alumina tube heated at 700°C., and when this is allowed to react with toluene/H₂ gas (e.g. 100seem), it is possible to obtain the carbon fiber having a structure asshown in the perspective view of FIG. 1C.

In this case, it is preferable that aspect ratio of the carbon nanotubeis in the range of 1:1000 to 1:10, and that aspect ratio of the carbonfiber is in the range of 1:5000 to 1:10. Also, it is preferable thatdiameter of the tubular or linear carbon structure is in the range ofabout 0.001 to about 0.5 micrometers and that its length is within therange of about 1 to about 5 micrometers.

Description will be given below on the present invention referring toembodiments of the invention by way of example and not limitation:

EXAMPLE 1

<Synthesis of Phosphoric Acid Type Fullerene Derivative(C₆₀═C(PO(OH₂)₂)>

First, a precursor C₆₀═C(PO(OEt)₂)₂ of a phosphoric acid type fullerenederivative was synthesized referring to the literature (Cheng, F; Yang,X; Zhu, H; and Song, Y: Tetrahedron Letters 41 (2000), pp.3947–3950).First, 1 g (1.39 mmol) of C₆₀ was dissolved in 600 ml of dehydratedtoluene. Then, 353 mg (1.39 mmol) of iodine and 2 g of Nal were added.By stirring up, 0.338 ml (1.39 mmol) of tetraethyl methylenediphosphonate was added. Under argon gas atmosphere, the mixture wasstirred up at room temperature for 24 hours and was then filtered. Theprecipitate was rinsed with a large quantity of CHCl₃. The solution thusobtained was dried in a rotary evaporator and was rinsed with a largequantity of alcohol. When the precipitate thus rinsed was dried up, aprecursor C₆₀═C(PO(OEt)₂)₂ of the phosphoric acid type fullerenederivative was obtained.

Then, 1 g of the precursor C₆₀═C(PO(OEt)₂)₂ of the phosphoric acid typefullerene derivative thus obtained was weighed, and this was stirred upin 50 ml of 1M NaOH solution at 60° C. for one hour to 30 hours forhydrolysis. When the solution thus obtained was subjected to proton ionexchange, phosphoric type fullerene derivative C₆₀═C(PO(OH)₂)₂ wasobtained.

The above synthetic reaction can be expressed as follows:

C₆₀+CH₂(PO(OEt)₂)₂→C₆₀═C(PO(OEt)₂)₂

-   -   →C₆₀═C(PO(ONa)₂)₂    -   →C₆₀═C(PO(OH)₂)₂

The number of the functional groups, which can be bonded to onefullerene cage as the base material can be controlled in the range of 1to 30 by adjusting molar ratio of the fullerene raw material forsynthesis and the other raw materials added to it. For instance, it ispossible to add the above functional groups to all of the double bondson fullerene molecule. The more the number of the functional groups onthe fullerene molecule is, the more the number of protons is increased,and the more the conductivity is increased.

FIG. 11 shows the results of measurement for FT-IR of the phosphoricacid type fullerene derivative C₆₀═C(PO(OH)₂)₂ obtained above. As shownin FIG. 11, strong peaks at 3440 cm⁻¹ and 1650 cm⁻¹ respectively appearto be the peaks due to the stretching vibration of O—H of water. Also,the peak at 1723 cm⁻¹ appears to be the peak when —OH group is directlybonded to C₆₀ when the specimen is hydrolyzed in NaOH. Further, strongand sharp peaks at 1210 cm⁻¹ and 1042 cm⁻¹ appear to be the peaks due toP═O and P—O.

EXAMPLE 2

<Synthesis of Phosphoric Acid Type Fullerene DerivativeC₆₀═(C(PO(OH)₂)₂)₂)>

First, 1 g (1.39 mmol) of C₆₀ was dissolved in 600 ml of dehydratedtoluene, and 706 mg (2.78 mmol) of iodine and 4 g of Nal were added.While stirring up, 0.676 ml (2.78 mmol) of tetraethyl methylenediphosphonate was added. Under argon gas atmosphere, the mixture wasstirred up at room temperature to 50° C. for 24 to 72 hours and wasfiltered. The precipitate was rinsed with a large quantity of CHCl₃. Thesolution thus obtained was dried up in a rotary evaporator and wasrinsed with a large quantity of alcohol. When the rinsed precipitate wasdried up, a precursor C₆₀═(C(PO(OEt)₂)₂)₂ of the phosphoric acid typefullerene derivative was obtained.

Next, 1 g of the precursor C₆₀═(C(PO(OEt)₂)₂)₂ of the phosphoric acidtype fullerene derivative obtained above was weighed, and this washydrolyzed in 50 ml of 1M NaOH solution at 100° C. for one hour to 30hours. The solution thus obtained was subjected to proton ion exchange,and a phosphoric acid type fullerene derivative C₆₀═(C(PO(OH)₂)₂)₂ wasobtained.

The above synthetic reaction can be expressed as follows:

C₆₀+2CH₂(PO(OEt)₂)₂→C₆₀═(C(PO(OEt)₂)₂)₂

-   -   →C₆₀═(C(PO(ONa)₂)₂)₂    -   →C₆₀═(C(PO(OH)₂)₂)₂

The result of measurement of FT-IR of the phosphoric acid type fullerenederivative C₆₀═(C(PO(OH)₂)₂)₂ showed main peaks similar to those peaksshown in FIG. 11 as prepared in Example 1.

EXAMPLE 3

<Thermal Analysis of the Phosphoric Acid Type Fullerene Derivatives ofExamples 1 and 2>

To determine thermal stability in each of the phosphoric acid typefullerene derivatives obtained in Examples 1 and 2, TG-DTA and RGA(residual gas analysis) were performed.

TG Measurement

TG-DTA measurement was performed on the phosphoric acid type fullerenederivative (the ratio of C₆₀>C<(PO(OH)₂)₂ (C₆₀) to >C<(PO(OH)₂)₂ was1:1). The measurement was performed under dry air atmosphere withtemperature increase rate of 5° C./min. The results are summarized inFIG. 12. As it is evident from FIG. 12, weight decrease occurs in nearlythree stages. Weight decrease from room temperature to the temperatureof about 300° C. was caused by water. Weight decrease from about 300° C.to 400° C. was estimated to be the result of decomposition of thespecimen. The final weight decrease was estimated to be the result ofdecomposition of fullerene.

RGA Measurement

The RGA measurement is the measurement of gas release from thedecomposition of the specimen. The measurement was performed undervacuum condition with temperature increase rate of 2° C./min. Theresults are shown in FIG. 13. The thin line at the uppermost portion ofFIG. 13 represents partial pressure of water. CO₂ and CO were detectedfrom 200° C. Also, the peak value of CO was obtained near 300° C.

As it is evident from FIG. 12 and FIG. 13, based on the results of themeasurement of TG and RGA, heat-resistant property of the phosphoricacid type fullerene derivative C₆₀>C<(PO(OH)₂)₂ was 200° C. or more. Itappears that the specimen began to gradually decompose from 200° C., andthe peak value was reached at 300° C.

EXAMPLE 4

<Preparation of Pellets of the Phosphoric Acid Fullerene Derivatives ofExamples 1 and 2>

The powder of each of the phosphoric acid type fullerene derivativesobtained in Examples 1 and 2 was pressed in one direction so thatpellets each in circular shape of 4 mm in diameter could be formed. Bothof the phosphoric acid type fullerene derivatives have good moldabilityand could be palletized easily without using the materials such asbinder resin. Each pellet was 300 micrometers in thickness, and we callthe pellets as pellets of Examples 1 and 2 respectively.

EXAMPLE 5

<Measurement of Proton Conductivity of the Pellets of the PhosphoricAcid Type Fullerene Derivatives of Examples 1 and 2>

Each side of each of the pellets of Examples 1 and 2 prepared in Example4 was sandwiched by metal plates, and AC voltage of 0.1 V was applied.At the frequency of 7 MHz to 1 Hz, AC complex impedance was measured.The measurement was performed under atmospheric air without humidifying.For impedance measurement, the proton conductive portion 1 of the protonconductor, which has pellets of Examples 1 and 2, electricallyconstitutes an equivalent circuit as shown in FIG. 14. Including theproton conductive portion 1 expressed by a parallel circuit of aresistance 5 and a capacitance 4, the capacitance 4 and the resistance 5are provided between a first electrode 2 and a second electrode 3. Thecapacitance 4 represents delay effect (phase delay in case of highfrequency) when protons are moved. The resistance 5 represents aparameter of easy movement of proton.

Here, the measurement impedance Z is expressed by Z=Re(Z)+i·1m(Z), andfrequency dependency of the proton conductive portion given by theequivalent circuit was determined.

The proton conductivity by calculation from AC resistance obtained fromcall-call plot (FIG. 15) was as follows: 1.8×10⁻⁴ S cm⁻¹ for the pelletsof the phosphoric acid fullerene derivative of Example 1, and 8.4×10⁻⁴ Scm⁻¹ for the pellets of the phosphoric acid type fullerene derivative ofExample 2. The conductivity of the pellets of the phosphoric acid typefullerene conductor of Example 2 was higher, and this may be attributedto the fact that there were more functional groups bonded to thefullerene molecules as the base material, and this results in moreprotons.

EXAMPLE 6

<Synthesis of Precursor C₆₀═(C(PO(OEt)₂)₂)_(n) of the Phosphoric AcidType Fullerene Derivative>

First, 1 g (1.39 mmol) of C₆₀ was dissolved in 600 ml of dehydratedtoluene. Then, 8.82 g (34.75 mmol) of iodine and 10 g of Nal were added.While stirring up, excessive quantity, i.e. 8.45 ml (34.75 mmol), oftetraethyl methylene diphosphonate was added. Under argon gasatmosphere, this was stirred up at room temperature to 50° C. for 24 to72 hours and was filtered. The precipitate was rinsed with a largequantity of CHCl₃. The solution thus obtained was dried up in a rotaryevaporator, and this was further rinsed with a large quantity ofalcohol. When the precipitate thus rinsed was dried up, a precursorC₆₀═(C(PO(OEt)₂)₂)_(n) of the phosphoric acid type fullerene derivativewas obtained. On C₆₀═(C(PO(OEt)₂)₂)_(n) thus prepared, MALDI-TOF-MS wasperformed. The value of n was 9 at maximum.

The above synthetic reaction can be expressed as follows:

-   -   C₆₀+12CH₂PO(OEt)₂)₂→C₆₀═(C(PO(OEt)₂)₂)₁₂

The number of the functional group, which can be bonded to the fullerenemolecule (e.g. C₆₀) as the base material can be controlled in the rangefrom 1 to 30 by adjusting molar ratio of the raw material serving as thebase material during synthesis and the other raw material added to it.For instance, it is possible to add the functional groups to all of thedouble bonds on the base material. The more the number of the functionalgroup on the base material is, the more the number of protons isincreased, and the more the conductivity is increased.

EXAMPLE 7

<Synthesis (1) of Sulfonic Acid Type Fullerene Derivative(C₆₀═(C(SO₃H)₂)_(n))>

First, 1 g (1.39 mmol) of C₆₀ was dissolved in 400 ml of dehydratedtoluene, and 3.53 g (13.9 mmol) of iodine and 5 g of Nal were added.While stirring up, excessive quantity, i.e. 2.96 g (13.9 mmol), ofmethane disulfonic acid chloride CH₂(SO₂Cl)₂) was added. Under argon gasatmosphere, this was stirred up at room temperature from 24 to 96 hours.When unreacted impurities were rinsed with a large quantity of toluene,diethyl ether and hexane, a precursor C₆₀═(C(SO₂Cl)₂)_(n) of sulfonicacid type fullerene derivative was obtained.

Next, 1 g of the precursor C₆₀═(C(SO₂Cl)₂)_(n) of the sulfonic acid typefullerene derivative was weighed, and this was stirred up in 100 ml of1M NaOH solution at room temperature for one hour to 30 hours forhydrolysis. The solution thus obtained was subjected to proton ionexchange, and the sulfonic acid fullerene derivative(C₆₀═(C(SO₃H)₂)_(n)) was obtained.

On the sulfonic acid type fullerene derivative (C₆₀═(C(SO₃H)₂)_(n))obtained above, measurement was made by MALDI-TOF-MS and elementanalysis was performed. As a result, the value of n was 4 to 6.

The above synthetic reaction can be expressed as follows:

C₆₀+_(m)CH₂(SO₂Cl)_(2→)C₆₀═(C(SO₂Cl)₂)_(n)

-   -   →C₆₀═(C(SO₃Na)₂)_(n)    -   →C₆₀═(C(SO₃H)₂)_(n)

FIG. 16 shows the results of measurement of FT-IR on the sulfonic acidtype fullerene derivative (C₆₀═(C(SO₃H)₂)_(n)) thus obtained. As it isevident from FIG. 16, strong peaks at 3436 cm⁻¹ and 1635 cm⁻¹ appear tobe the peaks due to O—H of water. Also, a strong peak at 1720 cm⁻¹appears to be the peak caused by direct bonding of —OH group with C₆₀when the specimen was hydrolyzed in NaOH. Further, strong peaks at 1232cm⁻¹ and 1026 cm⁻¹ seem to be the peaks due to S═O and S—O.

<Preparation of Pellets of the Sulfonic Acid Type Fullerene Derivativeof Example 7 and Measurement of Proton Conductivity>

Pellets of the sulfonic acid type fullerene derivative of Example 7 wereprepared by the same procedure as in Example 4. Each pellet had diameterof 4 mm and thickness of 1.12 mm. Each side of each pellet thus preparedwas sandwiched by metal plates, and AC voltage of 0.1 V was applied onit. AC complex impedance was measured with frequency of 7 MHz to 1 Hz.The measurement was performed in the atmospheric air withouthumidifying.

FIG. 17 shows a call-call plot. As shown in FIG. 17, linear call-callplot is a typical plot when proton conductivity of the specimen is high.The value of intersection of impedance real number portion is ACresistance. Proton conductivity calculated from this value was: 5.6×10⁻²S cm⁻¹. The conductivity was higher than that of the pellet of each ofthe phosphoric acid type fullerene derivatives of Examples 1 and 2, andthis was attributed to the fact that there were more functional groupsbonded to the fullerene molecule as base material, and hence, there weremore protons.

EXAMPLE 8

<Synthesis (2) of Sulfonic Acid Type Fullerene Derivative(C₆₀═(C(SO₃H)₂)_(n))>

First, 1 g (1.39 mmol) of C₆₀ was dissolved in 400 ml of dehydratedtoluene, and 3.53 g (13.9 mmol) of iodine and 5 g of Nal were added.While stirring up, excessive quantity, i.e. 3.22 g (13.9 mmol), ofmethane disulfonic acid diethyl ester, i.e. CH₂(SO₂OEt)₂, was added.Under argon gas atmosphere, this was stirred up at room temperature for24 to 96 hours. Unreacted impurities were rinsed with a large quantityof toluene, diethyl ether and hexane, and a precursorC₆₀═(C(SO₂OEt)₂)_(n) of sulfonic acid type fullerene derivative wasobtained.

Next, 1 g of the precursor C₆₀═(C(SO₂OEt)₂)_(n) of the sulfonic acidtype fullerene derivative thus obtained was weighed, and this wasstirred up in 100 ml of 1M NaOH solution at room temperature or at 50°C. for one hour to 30 hours for hydrolysis. The solution obtained wassubjected to proton ion exchange. On the sulfonic acid type fullerenederivative C₆₀═(C(SO₃H)₂)n obtained above, measurement was made byMALDI-TOF-MS and element analysis was performed. The value of n was 4 to6.

The above synthetic reaction can be expressed as follows:

C₆₀+mCH₂(SO₂OEt)₂→C₆₀═(C(SO₂OEt)₂)_(n)

-   -   →C₆₀═(C(SO₃Na)₂)_(n)    -   C₆₀═(C(SO₃H)₂)_(n)

Then, FT-IR was determined on this specimen, and the results were almostthe same as the results of FIG. 16 in Example 7. By the same procedureas in Example 7, pellets were prepared, and proton conductivity wasmeasured. The same value as in Example 7 was obtained.

The proton conductor according to the present invention, having a carbonderivative which has a carbon material selected from the groupconsisting of a fullerene molecule, a cluster consisting essentially ofcarbon, a fiber-shaped carbon and a tube-shaped carbon, and mixturesthereof; and at least a proton dissociative group, the protondissociative group being bonded to the carbon material via a cyclicstructure of tricyclic or more. Accordingly, its dependency on theatmosphere is low, and it exhibits high proton conductivity even indried air or under high temperature range, and it can be usedcontinuously.

The functional group has a group with proton-dissociating property, andit is bonded to the above substance via a cyclic structure of tricyclicor more. As a result, it is possible to improve heat-resistant propertyand to attain higher chemical stability.

By the method to manufacture the proton conductor according to thepresent invention, it is possible to manufacture the proton conductor ofthe present invention having excellent properties as described above ineasy and efficient manner, and it is also possible to reduce themanufacturing cost. Further, it is possible to synthesize the product onmass production basis.

In the electrochemical device of the present invention, a protonconductor sandwiched between a first electrode and a second electrodehas the above derivative, which serves as a proton conductor havingexcellent properties as described above. As a result, the same effectsas those of the proton conductor of the present invention can beattained, and no additional apparatus such as humidifier is required.Also, it is possible to design the system in compact size and in simplestructure.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A proton conductor comprising: a carbon derivative including a carbonmaterial selected from the group consisting of a fullerene molecule, acluster consisting essentially of carbon, a fiber-shaped carbon and atube-shaped carbon, and mixtures thereof, and at least one protondissociative group, the proton dissociative group being bonded to thecarbon material via a cyclic structure of tricyclic or more, wherein atleast one of the proton dissociative groups is —SO₃H.
 2. A protonconductor according to claim 1, wherein the fullerene molecule is aspherical carbon cluster molecule C_(m) where m is an integer selectedfrom the group consisting of 36, 60, 70, 76, 78, 80, 82, 84, 86, 88, 90,92, 94, 96 and combinations thereof.
 3. A proton conductor according toclaim 1, wherein at least an additional one of the proton dissociativegroups is selected from the group consisting of —PO(OH)₂, —SO₃H, and—COOH.
 4. An electrochemical device comprising: a first electrode, asecond electrode, and a proton conductor disposed between the first andsecond electrodes, wherein the proton conductor comprises a carbonderivative including a carbon material selected from the groupconsisting of a fullerene molecule, a cluster consisting essentially ofcarbon, a fiber-shaped carbon and a tube-shaped carbon, and mixturesthereof, and at least one proton dissociative group, the protondissociative group being bonded to the carbon material via a cyclicstructure of tricyclic or more.
 5. The electrochemical device accordingto claim 4, wherein the fullerene molecule is a spherical carbon clustermolecule C_(m) where m is an integer selected from the group consistingof 36, 60, 70, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96 andcombinations thereof.
 6. The electrochemical device according to claim4, wherein at least one of the proton dissociative groups is selectedfrom the group consisting of —PO(OH)₂, —SO₃H and —COOH.